1. Field of the Invention.
The present invention relates generally to gelable silicate solutions, and more particularly, to such solutions, their preparation and their use in oil field applications.
2. Description of the Prior Art.
In oil and gas well completion and remedial operations, cement compositions which set into hard substantially impermeable masses are commonly utilized. For example, in primary cementing, a cement composition, usually a hydraulic Portland cement composition, is pumped down a casing or liner disposed in a well bore and then upwardly into the annulus between the casing or liner and the walls of the well bore. Upon setting, the cement composition bonds the casing or liner to the well bore walls whereby the casing or liner is held in place and whereby interstitial voids in formations penetrated by the well bore are sealed and fluid communication or flow in the annulus is prevented.
A secondary remedial cementing process known as squeeze cementing is utilized to repair defects due to corrosion, failures in the primary cement and the like. In squeeze cementing operations, the problem area is isolated and a cement composition is forced into the annulus and/or portions of the formations penetrated by the well bore to provide seals therein.
In other applications, cement compositions are injected into subterranean formations to plug high permeability anomalies existing near the well bore. Such anomalies include fractures, thief zones and vugs which diminish the intended function of wells. For example, such anomalies diminish the performance of enhanced recovery injection wells by diverting the injected fluid away from hydrocarbon containing zones, and they diminish the performance of production wells by causing undesirable water production and the like.
As mentioned above, in carrying out the above described cementing processes, Portland cement compositions have most commonly been used. However, other cement compositions including mixtures of Portland cement and sodium silicate and other silica containing compositions have been utilized in oil field applications. For example, U.S. Pat. No. 3,146,828 issued Sep. 1, 1964 discloses a siliceous cement composition consisting of sodium silicate, a finely divided solid suspending agent, a siliceous aggregate, water and a stabilizing agent which forms a permeable solid upon setting. The permeable solid is utilized in wells to provide a barrier which prevents incompetent sands or the like from flowing into the well bore with produced hydrocarbons.
U.S. Pat. No. 4,014,174 issued on Mar. 29, 1977 discloses a method of strengthening the surface of a well bore and improving a subsequent Portland cement bond thereto by pretreating the zone to be cemented with an alkali metal silicate solution containing silica and causing the solution to form a gel therein.
U.S. Pat. No. 4,505,751 issued on Mar. 19, 1985 discloses a process for utilizing a silicate/silica cement composition in oil field applications. The cement composition is comprised of silica combined with an aqueous silicate solution which reacts over time to form a solid. The silicate/silica composition is utilized in well completion and remedial operations of the type described above.
While the above described and other aqueous silicate compositions have been utilized successfully in oil field applications, they generally include an alkali metal silicate such as sodium silicate which is relatively expensive. The alkali metal silicate can be utilized in liquid form, but liquid alkali metal silicate has the disadvantage that it freezes at a relatively high temperature and undergoes a chemical change upon being thawed. Dry alkali metal silicate compositions are also used, i.e., the dry components of a silicate composition such as dry sodium silicate, a dry solid filler and a dry buffer are mixed with water at the site of the well in which the silicate composition is to be used. A disadvantage of this procedure is that the dry solid materials are difficult to dissolve in the water, particularly when the water is at a relatively cold temperature.
Thus, there is a need for a less expensive source of alkali metal silicate which can be delivered to a well site in dry solid form and readily dissolved in cold water just prior to use.